A variety of portable heating cabinets suitable for heating food are known in the art. Ovens used in the catering industry, for example, allow cooking to be done in the oven at a location other than where the food is consumed. One portable oven design includes a removable heating unit which can be replaced with an insulating top which retains the heat supplied by the heating unit. The portable cabinet can be transferred from one location to another without loss of heat and has utility in any application where a portable heating or cooking unit is required.
One proposal for a food heating cabinet includes a top mounted unit for heating air and circulating the heated air throughout the cabinet. Heated air from the heating unit is forced into a plenum and then into the interior of the cabinet. Such a unit requires a source of heat and a mechanism for delivering heated air to the plenum. One method of heating the air is to convert an electric current into heat energy by joule heating.
It has been suggested, however, that joule heating with electric heating elements may not be the most efficient technique for heating the air. The electric potential energy conversion to heat and the subsequent transfer of this heat to air forced through the oven results in no better than a 50% conversion of the potential energy to useable heat energy. Conventional propane or natural gas sources of energy are no more efficient in heat generation. One goal therefore, in designing an oven for heating foods, be it portable or otherwise, is efficiency in converting latent fuel energy to heat energy.
A separate concern is control over the environment in which the food is cooked. It can be desirable, for example, to control the humidity of the air which contacts the food so that a desired end result is obtained. Control over conditions inside the oven is also important in test ovens where an inert or other controlled atmosphere is necessary and must be maintained throughout oven operation. It is apparent therefore that there exists a need to provide an energy efficient heating operation to both portable and stationary ovens where the environment inside the oven can be controlled.